Antarctic marine mammals and ocean acoustics

Marine mammals rely on sound and hearing as their primary means of communication and sensing their world. Concerns that anthropogenic sound in the ocean could infer their sensing, cause stress or even damage their hearing physically rose a controversial discussion and triggered a worldwide boost in marine bioacoustic research. Innovative acoustic technologies and field methods are required to provide a basis for carefully designed and technically challenging research projects on free-ranging marine mammals, especially under the harsh environmental conditions of polar regions. The Ocean Acoustics group within the Marine Observing Systems section endeavors multidisciplinary research of environmental scientists, geophysicists, oceanographers, physicists, physiologists, and biologists to investigate the need and scope of mitigation measures for the effects of man-generated sound in the ocean, develop acoustic census techniques, explore marine mammal responses to various anthropogenic sounds, and study the vocal behaviour and hearing physiology of Antarctic marine mammals

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

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Strange Sounds of the Southern Ocean

The waters around Antarctica host a unique and fantastic soundscape, dominated by ice and life. Large table icebergs are the largest moving objects on the planet, weighting up to 100 billion tons. Collisions with the shelf can release kinetic energy equalling that of a nuclear explosion and belong to the loudest events in the ocean. However, the chorus of the few remaining blue whales, the largest animal ever living on earth, is present every single minute of the year and cumulatively contributes the main component of the acoustic spectrum. Besides these two extremes, six years of continuous recordings from the ice borne Perennial Acoustic Observatory in the Antarctic Ocean (www.awi.de/PALAOA) yielded a wealth of different sounds, both of known and obscure origin. These passive acoustic recordings have already led to significant findings both in physics and biology and also about the impacts of human activities in this pristine area. However, making sense of unknown sounds is a big challenge. In fact, the most dominant sound of the Southern Ocean, present only during polar winter when observers are rare, is known for more than 40 years but remains a complete mystery yet. Can we solve that riddle just by listening indeed? A fundamental question pops up in this context: Is there a universal discrimination between signals of physical, biological and human origin

Natural Interpolation of Time Series

To interpolate data which is sampled in finite, discrete time steps into a continuous signal e.g. for resampling, normallya model has to be introduced for this purpose, like linear interpolation, splines, etc. In this paper we attemptto derive a natural method of interpolation, where the correct model is derived from the data itself, using somegeneral assumptions about the underlying process. Applying the formalism of generalized iteration, iteration semigroupsand iterative roots we attempt to characterize a method to find out if such a natural interpolation for agiven time series exists and give a method for its calculation, an exact one for linear autoregressive time seriesand a neural network approximation for the general nonlinear case

PALAOA An Autonomous SAM Device in the Atka Bay

The PerenniAL Acoustic Observatory in the Antarctic Ocean (PALAOA, Hawaiian whale) was set up on the Ekström ice shelf, Antarctica in December 2005 near the German Neumayer Station (Boebel et al., 2006). It is intended to record the underwater soundscape in the vicinity of the shelf ice edge over the duration of several years. These long-term recordings will allow studying the acoustic repertoire of whales and seals continuously in an environment almost undisturbed by humans. The data will be analyzed to (1) register species specific vocalizations, (2) infer the approximate number of animals inside the measuring range, (3) calculate their movements relative to the observatory, and (4) examine possible effects of the sporadic shipping traffic on the acoustic and locomotive behaviour of marine mammals. The data, which are largely free of anthropogenic noise, provide also a base to set up passive acoustic mitigation systems used on research vessels. Noise-free bioacoustic data thereby represent the foundation for the development of automatic pattern recognition procedures in the presence of interfering sounds, e.g. propeller noise

The Soundscape of the Southern Ocean – How Quiet and how Loud can Nature be?

The Southern Ocean around the Antarctic continent provides some of the most extreme environmental conditions on earth which shape also the unique underwater soundscape. The area probably contains the most quiet locations within the world's oceans but is also stage for some of the loudest natural events. It is still relatively void of anthropogenic noise and is one of the most important feeding grounds for great whales. However, comparatively little acoustic data exists from this region so far because the collection of acoustic recordings is hindered by logistic constraints associated with this remote region. Very Quiet The large cavities below the giant floating ice shelves of Antarctica are amongst the most isolated areas in the world - but with a window to the open sea. Neither local surface noise nor biological sources are present within hundreds of kilometers radius. Sound levels here should reflect unbiased readings of the long-range acoustic energy field - and yield a lower boundary of how quiet the ocean can get. During much of the year large parts of the polar oceans are covered by sea ice, which has a significant impact on the underwater acoustics. Sea ice isolates the water from the air, impeding the generation of waves, while the snow layer absorbs acoustic energy efficiently, creating an "anechoic chamber" which may serve as a natural lab to test and verify sound propagation models. Very Loud But ice is also a major source of noise. Table icebergs, calved from the shelf, are the largest moving objects on earth, spanning areas of 1000 square kilometers with a thickness of several hundred meters. Driven by the ocean currents, billions of tons of ice can gain terajoules of kinetic energy, equaling that of a nuclear bomb. This energy can be released within a brief period of time when the iceberg touches ground or collides with other bergs or the ice shelf. These events produce some of the loudest natural broadband sounds in the ocean, rivaled only by earthquakes and can be recorded in distances as far as other continents. They would probably make perfect test signals to measure long range broadband sound propagation. However, their occurrence is relatively sparse, we detect about one or two such events in the vicinity of our Antarctic observatory per year. Additionally, smaller but frequent iceberg calving events, reaming of ice floes, exploding little bubbles of high pressure gas occlusions in melting glacier ice combine to a most diverse abiotic soundscape. Relevant Biology However, it is the biology that produces the major contribution to the overall sound budget here. Despite the reduction of the blue whale population to a small fraction of their pre whaling size, the chorus of blue whales is the predominant acoustic source in the Southern Ocean, present on 365 days per year. Together with about ten other marine mammal species occupying this ocean area, they fill the whole audible frequency range with relatively little spatio-temporal overlap, suggesting that acoustic bandwidth is an important natural resource that different species compete for. Here we have the unique chance to study the acoustic ecology of a large ecosystem which is not yet significantly influenced by anthropogenic sound and resides in an extremely rich natural soundscape. And as many of its acoustic ingredients compare to anthropogenic emissions in other areas of the world, one could derive reference models of the interaction of sound and biology from here. Data Acquisition All this is based on long term, wide area and high quality passive acoustic data. Our current effort builds on an established network of oceanographic moorings in the Weddell sea, which is fitted with long term acoustic recorders capable of recording broad band audio continuously for several years. Along with the permanent acoustic observatory on the ice shelf, PALAOA, which features a hydrophone array protected under a 100 m thick ice shield, this covers a significant part of the Weddell basin from the shore to the deep sea. Sea ice coverage and ice berg movement is captured by high resolution satellite images and local ship traffic is monitored by AIS receivers. Our acoustic record spans 6 years by now will be continued to be able to characterize typical annual fluctuations and long term trends in both the acoustic background and animal behavior and set them in relation to abiotic factors. We believe that this dataset will serve as a valuable reference for many ocean noise related questions and encourage to set up a similar networks in other polar seas

Audiometric procedures in yearling southern elephant seals of Marion Island

The audible frequency ranges and corresponding hearing thresholds are the most characteristic properties of any auditory system. They are typically displayed in the form of an audiogram as the function of minimal audible sound level in respect to frequency. For about 90% of marine mammal species including all Antarctic seals audiograms have not been measured as yet, and knowledge about their hearing is limited to assumptions based on measurements on similar species and frequency ranges of their own vocalisations, with the underlying assumption that vocalisation frequencies correspond with hearing abilities. However, it is well known that hearing is possible in excess of up to several octaves beyond the vocalisation frequencies since hearing has not only evolved as a function of communication; and marine mammals in particular have evolved to use sound and hearing as their primary means of perceiving their surroundings. Recordings of vocalisations related to reproductive or feeding behaviour as well as measurements of hearing abilities are therefore very relevant to interpret population ecology as well as several other aspects of seal biology.We used electro-encephalography to measure auditory evoked potentials, especially the auditory brainstem responses of immobilised southern elephant seal yearlings. The field study was conducted at the haulout sites of elephant seals close to the Marion Island Research Base (46°54S, 37°45E) from 12 to 24 April 2007. Five 1.5 years old seals were chosen for experiments. We developed a portable experimental set-up in order to test for basic audiogram data. The experiment was focussed on a mapping procedure to identify areas on the seals head most suitable for AEP recordings by seeking for optimal electrode placements, where signal to noise ratios are best. The poster shows the methodological approach, presents first results on audiometric procedures on southern elephant seals, and discusses the ecological relevance of audiometric investigations